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Full text of "A new species of tree squirrel (Sundasciurus) from Palawan Island, Philippines (Mammalia: Sciuridae)"

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PROC. BIOL. SOC. WASH. 
92(2), 1979, pp. 280-286 



A NEW SPECIES OF TREE SQUIRREL 
(, SUNDASCIURUS ) FROM PALAWAN ISLAND, 

PHILIPPINES 

(MAMMALIA: SCIURIDAE) 

Lawrence R. Heaney 

Abstract . — A new tree squirrel, Sundasciurus rabori, new species, from 
the mountains of Palawan Island, Republic of the Philippines, is named and 
described. It is assigned to the subgenus Aletesciurus on the basis of cranial 
characters and morphometries. Relationships of taxa within the genus are 
considered briefly. 



In 1962, an expedition sponsored by the U.S. Naval Medical Research 
Unit No. 2, Bernice P. Bishop Museum of Honolulu, and the Silliman Uni- 
versity of Dumaguete City, Republic of the Philippines, collected verte- 
brates on Palawan and nearby smaller islands in the southwestern portion 
of the Philippines (Kuntz, 1969). Among the 863 mammals obtained, all of 
which are now deposited at the National Museum of Natural History, Smith- 
sonian Institution (USNM), are five squirrels representing an undescribed 
species that differs markedly from all other Philippine tree squirrels. This 
paper describes this new species and briefly documents its relationship to 
other members of the genus Sundasciurus. 

Methods 

Cranial measurements were made with dial calipers graduated to one- 
twentieth of a millimeter (mm). All capitalized color names are from Ridg- 
way (1912). All measurements are as defined in DeBlase and Martin (1974) 
except the following: rostral depth, taken from the point where the maxil- 
lary-premaxillary suture crosses the midline on the ventral surface of the 
rostrum, to the closest point on the midline of the dorsum of the rostrum; 
rostral length, taken from the anteriormost point of the nasals at the midline 
to the closest point in the orbit; orbital length, taken from the point in the 
orbit where the preceding measurement was taken (i.e., the anteriormost) 
to the most posterior point in the orbit (see Moore, 1959:164); palatal 
breadth, taken from the labial edges of P4; length of diastema, taken along 
the midline from the posterior margin of the incisors to the line defined by 
the anterior points of the maxillary toothrow. External measurements shown 
in Table 1 were taken from specimen labels. For S. hippurus and S. brookei 
the total length shown is the sum of head and body length plus tail length, 



VOLUME 92, NUMBER 2 



281 



as recorded by the collector. A cluster analysis (BMDP2M) and principal 
components analysis (BMDP4M) were performed on a Honeywell 66-60 
computer at the University of Kansas. Comparisons of taxa are based on 
specimens at the USNM, but data used in compiling Table 1 were also 
obtained from specimens housed in the Field Museum of Natural History 
(FMNH), as noted in the text. 

Sundasciurus rabori, new species 

Holotype. — Adult male represented by skin and skull, USNM 477989. 
Obtained 16 April 1962 at Magtaguimbong, Mt. Mantalingajan, Palawan Is- 
land, Republic of the Philippines, between 3,600 and 4,350 ft elevation by 
D. S. Rabor; this is approximately 8°48'N, 117°40'E. Skull complete and 
unbroken; skin well prepared, with terminal portion of tail missing, though 
the external measurements taken by the collector were probably taken prior 
to this loss. 

Specimens examined . — Skins and skulls of five individuals, all from the 
type locality, USNM 477985-477989. Numbers 477985 and 477989 are 
adults; the skull of 477985 is crushed. Numbers 477986-477988 are in adult 
pelage but had not completed growth, as indicated by thin cranial bone and 
open basioccipital sutures; I consider these subadults. 

Measurements . — External measurements of the holotype, the second 
adult male, and the mean for the three subadults, all taken from the labels 
made out by the collector, and my cranial measurements are listed in Table 1 . 

Diagnosis . — Dorsal and lateral fur dense and soft, mostly 15 mm long, 
colored a dark brown agouti. Terminal bands black, subterminal bands cor- 
responding most closely to Ochraceous Orange, and basal bands black. 
Subterminal bands of hair on nose paler than elsewhere, corresponding to 
Pale Yellow-Orange. Color of the hair on the ears and around the eyes not 
different from that of the surrounding hair. Ventral region, especially within 
1 cm of the midline from the throat to the anal region, and ventral surface 
of the limbs washed with silver, corresponding to Light Buff. Tail fur agouti 
with three alternating bands of Ochraceous Orange and black, and tipped 
with Pale Yellow-Orange. Skull (Fig. 1) relatively gracile; rostrum slender; 
postorbital region short; temporal ridges not fused to form a sagittal crest; 
posterior portion of the cranium domed, not curving evenly to the occipital 
crest; palate narrow, strongly concave. Bullae small, with a single septum 
which is divided to form a small anteromesial lobe, with no portion con- 
spicuously inflated. 

Additional specimens examined. — S. h. hippurus (6), Gunong Tebu (350 
ft), Trengganu, West Malaysia, USNM 311342-311345, Bukit Besi, Treng- 
ganu, West Malaysia, USNM 311346-311347; S. hoogstraali (10), 6 km NE 
San Nicolas, Busuanga Island, USNM 477850-477857, 477860, 477862; 5. 



282 



PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 





Fig. 1. Ventral and dorsal views of the skull of the holotype (USNM 477989) of Sundasci- 
urus rabori, approximately twice life-size. 



juvencus (23), Tarabanan, Concepcion, Puerto Princesa, Palawan Island, 
USNM 477879-477883, 477890-477898, 477902-477910; 5. mindanensis (2) 
Loreto, Surigao del Norte, Dinagat Island, USNM 462199-462200; S. mol- 
lendorffi (2), 6.5 km SW Culion, Culion Island, USNM 477946-477947; 5. 
samarensis (16), Samar or Leyte Island, USNM 105464-105465; Matugui- 
nao, Samar Island, FMNH 87722-87726, Mt. Capoto-an, Samar Island, 
FMNH 87728-87736; S. steerii (21), Minagas Point, Dalawan Bay, Balabac 
Island, USNM 477964-477984; S. brookei (2), Poring, Ranau National Park, 
Sabah, USNM 488399-488400; S. j. jentincki (7), Lumu Lumu, Mt. Kina- 
balu, Sabah, USNM 292570-292576; S. I. lowii (5), Sungei Djambajan, Bor- 
neo, USNM 198739, 198744-198745, Ranau, Sabah, USNM 300988-300989, 
S. t. tenuis (10), 16 km N Kuala Lumpur on Pahang Road, Selangor, West 
Malaysia, USNM 283482-283483, 290160-290167. 

Comparisons . — Moore (1958) named the genus Sundasciuriis on the basis 
of characters of the bulla, noting that his classification showed some cor- 
respondence with that of Thomas (1915) based on the structure of the bac- 





VOLUME 92, NUMBER 2 283 



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Taxon 


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284 



PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 




S. mindanensis 
S somorensis 
S. steerii 
S. mollendorffi 
S. juvencus 
S. hoogstraa/i 
S. rabori 
S. hippurus 
S. brookei 
S. lowii 
S. jentincki 
S. tenuis 



1 1 1 1 1 1 

6.0 5.0 4.0 3.0 2.0 LO 

Amalgamation Distance 

Fig. 2. Cluster phenogram of morphometric similarity of 12 species of Sundasciurus, based 
on data in Table 1. 



ulum. He divided the genus into two subgenera. The subgenus Aletesciurus 
included all named Philippine forms, as well as S. hippurus from the Sundaic 
Subregion. Diagnostic features are their larger size (skull length over 50 mm 
according to the original description, but over 45 mm according to Moore, 
1959), presence of an inconspicuous anteromesial lobe in the bulla, and 
presence of a sagittal crest in adults. The nominate subgenus contained four 
species, all from the Sundaic Subregion, which have skull lengths under 40 
mm, an inflated anteromesial lobe, and no sagittal crest. 

Sundasciurus rabori is intermediate in size between the two subgenera as 
defined by Moore (1958), although closer to Aletesciurus (Table 1). In com- 
mon with the small species, S. rabori lacks a sagittal crest; in most sciurids 
I have examined there is a positive allometric relationship between size and 
development of the cranial crest, and I hesitate to use the crest as an indi- 
cator of relationship without further study. Each bulla of S. rabori has a 
small anteromesial lobe which is inflated more than in S. hippurus or the 
Philippine forms, but is conspicuously less inflated and less sharply defined 
than in the smaller Sundasciurus. Moore (1959) found that the structure of 
the bulla was a consistent and useful character for discerning relationships 
among diurnal squirrels. I conclude that, although intermediate in some 
ways, S. rabori is more similar to the subgenus Aletesciurus than Sunda- 
sciurus on the basis of the discrete characters available. 

To investigate the relationships of S. rabori further, I studied the phenetic 



VOLUME 92, NUMBER 2 



285 



similarity of 12 taxa using a cluster analysis based on the cranial measure- 
ments in Table 1, using only the type of S. rabori for this analysis. The 
resulting phenogram (Fig. 2) supports the division of Sundasciurus into two 
subgenera as defined by Moore (1958) and discussed above. Within the 
subgenus Aletesciurns the greatest difference is between S. hippurus and 
the Philippine members of the subgenus. S. rabori is most similar to the 
lowland Philippine squirrels, which are themselves divisible into a southern 
Philippine group (containing S. mindanensis and samarensis, and probably 
S. philippinensis and S. davensis — not examined), and a Palawan group 
(containing S. hoogstraali, S. juvencus, S. mollendorffi, and S. steer'd). It 
is possible that the southern Philippine group and the Palawan group each 
represent a species with several subspecies, but further analysis is required 
before this taxonomic change can be justified, and listing of S. juvencus as 
a subspecies of S. steerii by Kuntz (1969) is premature. 

I conclude from the above analyses that S. rabori is most closely related 
to the other Sundasciurus from the Philippines, and should be assigned to 
the subgenus Aletesciurus. 

A principal components analysis identified length of the diastema, orbital 
length, rostral depth, length of the maxillary molariform toothrow, and pal- 
atal breadth as the five measurements most useful for distinguishing among 
all taxa. S. rabori was characterized by this analysis as having a relatively 
short toothrow, narrow palate, long diastema and orbit, and deep rostrum. 

Remarks. — Although specimens of S. rabori have been taken only on Mt. 
Mantalingajan, which is the highest mountain on Palawan at 6,841 ft (2,085 
m), they may occur widely on Palawan at elevations above 1,100 m, which 
is the elevation at which a major vegetational change takes place in most of 
Southeast Asia (Medway, 1972; Steenis, 1964). Regions above this elevation 
include substantial areas in the Mantalingajan Range, Victoria Range, and 
Cleopatra Needle. No other island in the Palawan chain has mountains over 
765 m. No information is available regarding the ecjlogy of this species. 

Etymology. — This species is named for its collector, Dr. Dioscoro S. Ra- 
bor, in recognition of his contributions to knowledge of the vertebrates of 
the Philippines. I suggest “Palawan montane squirrel” as an English name. 

Acknowledgments 

This paper benefited from suggestions and editorial comments from Greg- 
ory Glass, Robert Hoffmann, James Koeppl, Thomas McIntyre, Gary Mor- 
gan, Guy Musser, Richard Thorington, and Robert Timm. Partial support 
was provided by the Smithsonian Institution Office of Awards and Grants. 
Computer facilities were provided by the Academic Computer Center of the 
University of Kansas. Richard Thorington and Patricia Freeman provided 
access to specimens housed in the USNM and FMNH, respectively. 



286 



PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 



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